Opponents of fracking have highlighted concerns about potential water contamination and environmental damage, as well as small-scale earthquakes.

Campaigners have been erecting marquees, tents, kitchen and toilet facilities on the site, about a mile from the exploratory drilling project.

Cuadrilla, which has said it is unlikely to turn the site into a fossil fuel production area, has scaled back its operation amid fears of unrest.

One activist, Luke Johnson, said: "Cuadrilla's announcement they'll halt drilling is already a victory for us, but it's only a start. We would like to make sure they don't frack in Balcombe, or anywhere else at all."

James Basin, 31, said: "I think Cuadrilla are keeping their heads down. I wouldn't be surprised if they have just broken one of their drills.

"We are expecting quite a few more people to arrive from London, and obviously we will be visiting the site to see what a mess Cuadrilla has made of it."

Razor-topped fences surround the drilling site as camp organisers No Dash for Gas warned there will be "direct action" in the days ahead.

Already around 40 people have been arrested since the anti-fracking protests sprang up on the outskirts of the West Sussex village three weeks ago.

No Dash for Gas said the camp programme will include skills-sharing in campaign building and direct action, as well as talks, assemblies and workshops.

Francis Egan, chief executive of Cuadrilla, has voiced concern about safety on the site and called on protesters intent on breaking the law: "Please don't do it."

He told ITV News: "I'm quite worried about safety on the site.

We have a group who are relocating a camp to the site, who have said publicly that they will be taking direct action against the site.

"It's a small site. There are a small amount of workers on the site. We are doing something that is legally approved and I am worried about the safety implications for our workers, for peaceful protesters."